1. Field of the Invention
The present invention relates to a content playback system, a playback device, a playback control method, and a program.
2. Description of the Related Art
Known related art provides a content playback system which plays back content by transferring audio and image content stored on a server to a client (playback device) through a network between the client and the server that are provided with communication functions, in accordance with the Transmission Control Protocol/Internet Protocol (TCP/IP). In the content playback system, first, the client generally issues a request to the server to search for content that can be played back and to transmit a list of the content that can be played back. In response to the request, the client receives from the server the list of the content that can be played back. The client is also able to request that the server transmit the content that a user selects from the list, and can receive and playback the content that the server transmits in response.
As the content data is transmitted by streaming from the server, the client sequentially stores (buffers) the content data in a buffer memory temporarily. At a point when a specified amount of the data has been stored, the client reads the content data from the buffer and starts playing back the content. In a case where the client can handle only uncompressed digital data, the server decodes (expands) compressed digital data that has been compressed and encoded by an encoding system such as MPEG1 Audio Layer 3 (MP3) or the like, converts the data into uncompressed digital data, such as linear PCM data or the like, and transmits the data to the client.
Note that, in the above-described content playback system, the same content can be received from the server and played back in synchronization by a plurality of the clients that are connected to a network. For example, it is conceivable that when a house party or the like is held at a user's home, a home network system including a client provided in a living room and a client provided in a bedroom could be used to play back the same music in synchronization by the clients in the living room and the bedroom.
According to Japanese Patent Application Publication JP-A-2006-237918, a method for achieving synchronized playback by multiple clients is disclosed. In this method, the same content is simultaneously delivered to multiple clients by a server by using multicast (for example, a user datagram protocol (UDP) multicast), and the multiple clients play back the content in synchronization. In this case, to achieve highly accurate synchronized playback, each client must be informed of a playback timing. According to the technology disclosed in JP-A-2006-237918, time management (such as playback timing calculation and notification) for synchronized playback is performed on the server side (such as an HDD recorder).